1. Field of the Invention
The present invention pertains to an apparatus for deactivating a pump, such as a downhole progressing cavity pump, when a fluid level on the inlet side of the pump is insufficient.
2. Discussion of the State of the Art
There are many commercially available suction pumps that may be damaged when the fluid level on the inlet side drops below a certain level. Such pumps are used in a wide variety of applications, and one example is the use of a progressing cavity down-hole oil pump for pumping oil from the ground.
The progressing cavity down-hole oil pump is installed in a well and the drive head, which is mounted at the wellhead, rotates a rotor which in turn displaces fluid from a stator, up through tubing, and to the wellhead at the surface. Oil, water and gas pass from the wellhead through a flowline to a treating and storage facility.
When an underground reservoir fails to provide sufficient oil and water to keep the pump suction covered, a situation commonly known as a "pumped off" condition arises. The progressing cavity pump operating under this condition for very long will become damaged. Further, at least in an oil well application, the liquid is often surging in a pumped-off condition, and a pump shut-down may be triggered prematurely by the retreating stage of a surge cycle. There is a need in the art for a pump-off control system that will stop a suction pump in a low-flow situation and will not be triggered prematurely in a surging situation.
In order to solve the problem of deactivating a pump when a pumped-off condition exists, an object of the present invention is to provide a low-flow pump-off control that causes a pump motor to be shut off when there is an insufficient flow of fluid to an inlet side of the pump.
It is a further object of the invention to provide a low-flow pump-off control that causes the motor to be shut off when the low flow of fluid to the pump inlet threatens to damage the pump.
It is a further object of the invention to provide a low-flow pump-off control that will not shut off a pump motor prematurely during a retreating stage of a surge cycle.
It is a further object of the invention to provide a low-flow pump-off control that will not fail to shut off a pump motor because a low flow situation is continuously interrupted by brief intervals of sufficient flow.
It is a further object of the invention to provide a low-flow pump-off control that generates a differential pressure in a series of stages and provides a passage for gas that is different from a passage for liquid.
It is a still further object of the invention to provide a low-flow pump-off control that is controlled by a differential pressure switch wherein a differential pressure indicative of an adequate flow rate is employed that is sufficiently different from a differential pressure indicative of an inadequate flow rate.
Other objectives of and additional problems solved by the present invention will become apparent from the following detailed description.